ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-10-365-2010The impact of dust on sulfate aerosol, CN and CCN during an East Asian dust stormManktelowP. T.1CarslawK. S.1MannG. W.1SpracklenD. V.11School of Earth and Environment, University of Leeds, Leeds, UK18012010102365382This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/10/365/2010/acp-10-365-2010.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/365/2010/acp-10-365-2010.pdf

A global model of aerosol microphysics is used to simulate
a large East Asian dust storm during the ACE-Asia
experiment. We use the model together with size resolved
measurements of aerosol number concentration and composition
to examine how dust modified the production of sulfate aerosol
and the particle size distribution in East Asian
outflow. Simulated size distributions and mass concentrations
of dust, sub- and super-micron sulfate agree well with
observations from the C-130 aircraft. Modeled mass
concentrations of fine sulfate (<i>D<sub>p</sub></i>&lt;1.3 &mu;m)
decrease by ~10% due to uptake of sulfur species onto
super-micron dust. We estimate that dust enhanced the mass
concentration of coarse sulfate (<i>D<sub>p</sub></i>&gt;1.0 &mu;m) by
more than an order of magnitude, but total sulfate
concentrations increase by less than 2% because decreases
in fine sulfate have a compensating effect. Our analysis shows
that the sulfate associated with dust can be explained largely
by the uptake of H<sub>2</sub>SO<sub>4</sub> rather than reaction of
SO<sub>2</sub> on the dust surface, which we assume is suppressed
once the particles are coated in sulfate. We suggest that many
previous model investigations significantly overestimated
SO<sub>2</sub> oxidation on East Asian dust, possibly due to the
neglect of surface saturation effects. We extend previous
model experiments by examining how dust modified existing
particle concentrations in Asian outflow. Total particle
concentrations (condensation nuclei, CN) modeled in the dust-pollution plume are
reduced by up to 20%, but we predict that dust led to less
than 10% depletion in particles large enough to act as
cloud condensation nuclei (CCN). Our analysis suggests that E. Asian
dust storms have only a minor impact on sulfate particles
present at climate-relevant sizes.